Reactor and process for preparing hydrogen sulphide

ABSTRACT

The present invention relates to a reactor and to a process for synthesis of hydrogen sulphide from elemental sulphur and hydrogen at elevated pressure and elevated temperature. The invention further relates to the use of the reactor for preparation of hydrogen sulphide in high yield and with a low H 2 S x  content.

The present invention relates to a reactor and to a process forsynthesis of hydrogen sulphide from elemental sulphur and hydrogen atelevated pressure and elevated temperature. The invention furtherrelates to the use of the reactor for preparation of hydrogen sulphidein high yield and with a low H₂S_(x) content.

Hydrogen sulphide is an industrially important intermediate, for examplefor the synthesis of methyl mercaptan, dimethyl sulphide, dimethyldisulphide, sulphonic acids, dimethyl sulphoxide, dimethyl sulphone, andfor numerous sulphidation reactions. It is nowadays obtainedpredominantly from mineral oil and natural gas processing, and byreaction of sulphur and hydrogen.

Hydrogen sulphide is prepared from the elements typically byintroduction of gaseous hydrogen into a sulphur melt, by convertingsulphur to the gas phase and converting it therein in an exothermicreaction with hydrogen to hydrogen sulphide (Ullmann's Encyclopedia ofIndustrial Chemistry, Sixth Edition, 1998, Wiley-VCH).

In order to achieve a satisfactory reaction rate and a high hydrogensulphide yield, the reaction has to take place at elevated temperaturerelative to standard conditions. According to the further use intended,it may be necessary to provide the hydrogen sulphide prepared at apressure of >5 bar. In this case, it would be advantageous to performthe hydrogen sulphide synthesis directly at the pressure required. Thisentails a further temperature increase in order to ensure thatsufficient sulphur is converted to the gas phase. However, theperformance of the hydrogen sulphide synthesis at a temperature of >450°C. has the disadvantage that hydrogen sulphide causes corrosion damageto the reactor material under these conditions. There is accordingly arequirement for a reactor construction which enables high conversionrates and simultaneously avoids damage, at least to the pressure-bearingelements of the reactor.

One approach to enhancing the hydrogen sulphide yield is to increase theresidence time of the hydrogen gas in the sulphur melt. This is done,for example, in U.S. Pat. No. 2,876,070 and DE 10 2008 040 544 A1 by useof reactors having gas collecting regions in the form of intermediatetrays or cups arranged within the sulphur melt. However, this type ofconstruction achieves a conversion of hydrogen of only >96%. Increasingthe number of gas collecting regions could perhaps enhance theconversion, but this would have the disadvantage that a greater reactorvolume would be required.

The principle of increasing the residence time of the hydrogen gas inthe sulphur melt is also accomplished in DE 10 2008 040 544 A1 by areactor having a bed of random ceramic packings in the sulphur melt.This reactor achieves a conversion of >99%. However, this reactor designrequires constant hydrogen supply, since, in the event of a decline orshutdown in the hydrogen supply, the reaction gas can escape completelyfrom the region of the random packing bed, and the random packing bedcan become filled with liquid sulphur. Such a reactor can therefore beoperated only within a very narrow load range.

A further means of enhancing the reaction rate is the use of catalysts,for example oxides or sulphides of cobalt, nickel or molybdenum. Thisapproach is disclosed, for example, in U.S. Pat. No. 2,863,725 and EP 2125 612 B1 in the form of reactors having catalyst-filled tubes whichdip into the sulphur melt, and the gaseous reactants flow through them.However, disadvantages of these reactors are found to be that they areoperated at a pressure of <5 bar, and that, as a result of the fact thatthe reaction of sulphur and hydrogen is predominantly catalytic, a largeamount of catalyst is required.

It is therefore an object of the present invention to provide a reactorfor preparation of hydrogen sulphide from sulphur and hydrogen, whichensures a high hydrogen conversion and a high purity of the hydrogensulphide produced. The reactor should also enable the preparation ofhydrogen sulphide at a pressure of >5 bar, have a very compact designand ensure a very wide load range. Especially in an integratedproduction system, a very wide load range is advantageous, in order tobe able to react flexibly to variations in load, rather than having todispose of excess amounts which are not required by the integratedsystem at that moment but result from inflexibility. Finally, thereactor, from the point of view of costs, maintenance and safety, shouldbe less prone to corrosion damage under the intended operatingconditions. With regard to the energy which is required for provision ofthe sulphur melt and for dissipation of the heat of reaction, aparticularly efficient reactor design is additionally desired. Inaddition, minimization of the amount of catalyst required andmaximization of the catalyst service life is desirable.

To achieve this object, the present invention provides a reactorsuitable for continuous preparation of hydrogen sulphide by exothermicreaction of sulphur and hydrogen to form a final product gas mixtureP_(final) comprising hydrogen sulphide and sulphur at elevatedtemperature and elevated pressure relative to standard conditions, saidreactor comprising

-   -   a lower reactor region suitable for accommodating a sulphur        melt, and    -   a gas collecting region suitable for accommodating the product        gas mixture P_(final) at elevated temperature and elevated        pressure relative to standard conditions.

The reactor according to the invention is characterized in that itadditionally comprises at least two non-pressure-bearing first cavernsand at least one supply device suitable for controlled supply ofpressurized gaseous hydrogen per first cavern, said caverns beingsuitable for at least temporary accommodation of a product gas mixtureP₁ which forms in exothermic reaction and comprises hydrogen sulphide,sulphur and hydrogen, and the reactor comprises one or morenon-pressure-bearing second cavern(s) which are arranged above the firstcavern(s) and are suitable for at least temporary accommodation of theproduct gas mixture P₁ formed in the first cavern(s) and for formationof further hydrogen sulphide by exothermic reaction of sulphur andhydrogen to form a product gas mixture P₂.

The hydrogen supply devices are designed such that the first caverns canbe supplied with hydrogen independently of one another. The amount ofsulphur and hydrogen which is fed into an individual cavern can thus beset separately for each first cavern. This enables, for example, areduction in hydrogen sulphide production by shutting down the hydrogensupply to one or more first caverns. The reaction in the first cavern(s)remaining may continue at constant hydrogen concentration and henceunder constant reaction conditions. Alternatively, with constant totalamount of hydrogen introduced, the hydrogen load can be distributedbetween several caverns or concentrated in individual caverns in orderto influence the reaction conditions in the first caverns in acontrolled manner.

The reactor comprises an outer, pressure-bearing vessel. The latterpreferably has the shape of an upright cylinder closed by a hood at eachof the two ends. A reactor according to the invention has a volume ofpreferably 0.5 to 200 m³. The reactor according to the invention alsohas one or more supply devices suitable for supply of liquid sulphur.

The supply devices for introduction of hydrogen are preferably at thelower end of the reactor, such that the gaseous reactants flow throughthe reactor along the longitudinal axis thereof.

The hydrogen introduced into the sulphur melt is saturated with gaseoussulphur and is accommodated by the first caverns. In the gas space ofthe first caverns, hydrogen and sulphur are converted in exothermicreaction to hydrogen sulphide, forming the product gas mixture P₁comprising hydrogen, sulphur and hydrogen sulphide. The caverns arepreferably surrounded by the sulphur melt, such that the heat ofreaction released in the caverns is dissipated into the sulphur melt.

A “cavern” in the context of this invention is understood to mean anystructural device that can accommodate and hold a gas volume. A cavernmay take the form, for example, of a hood-shaped installed device underwhich a particular gas volume can collect and flow over the outer edgesof the hood shape, which is open in the downward direction, to higherreactor regions. In a further illustrative embodiment, a cavern may beformed by beds of hollow bodies or random packings at different levels.For example, these hollow bodies or random packings may take the form ofbeds on screens or screen boxes. Suitable hollow bodies or randompackings are, for example, straight or curved hollow cylinders, hollowspheres, deformed hollow spheres, bell-shaped bodies, saddle-shapedbodies, screw-shaped bodies or other three-dimensional bodies withindentations and/or openings. In order to enable the penetration of thegas into the cavities of the hollow bodies or random packings, thehollow bodies and random packings preferably have orifices in theirouter wall and/or are manufactured from porous material. A bed of thehollow bodies and random packings according to the invention preferablyhas a useful porosity (open porosity) φ_(open) of more than 0.32, morepreferably more than 0.40, most preferably more than 0.6.

In a preferred embodiment, a cavern consists of a horizontalintermediate tray having one or more orifices through which the gas canflow into higher reactor regions. Along the edges of the orifices, theintermediate tray has weirs running vertically downward, which retain acertain gas volume in the cavern. FIG. 3 shows some illustrativeembodiments of caverns useable in accordance with the invention.

The use of caverns in the form of hood-shaped installed devices or inthe form of the above-described horizontal intermediate trays isgenerally preferable to the use of caverns in the form of beds of hollowbodies or random packings. A disadvantage of hollow bodies or randompackings may be that deposits of reaction by-products may occur overprolonged reactor run time under particular conditions, which couldblock the hollow bodies or random packings. The use of caverns in theform of hood-shaped installed devices or in the form of horizontalintermediate trays is suitable for avoiding this potential disadvantageand may therefore contribute to an extension of the reactor servicelife. Moreover, this cavern design facilitates the adjustment of theresidence time of the gaseous reactants in the caverns, since parameterssuch as the ratio of height to width of the cavern volume, for example,are easier to calculate and to alter.

A further advantage of this cavern design is that the reaction gasitself, in the event of reduced hydrogen supply, does not completelyescape from the caverns, and that a reduction in the hydrogen supplyleads to an extension of the residence time. This residence timeextension is suitable for compensating for a decrease in the reactiontemperature owing to lower hydrogen supply and thus enabling aconstantly high conversion. Caverns in the form of hood-shaped installeddevices or in the form of intermediate trays therefore considerablywiden the acceptable load range of the reactor.

The load range of the reactor may thus be within a range from 0 to 4000m³ (STP) (H₂)/(m³ (cavern volume)·h). The cavern volume relates in eachcase to a cavern through which gas flows.

The “first cavern” in the context of this invention refers to a cavernif the gas mixture which is collected in the cavern in question has notalready flowed through other caverns beforehand.

In an alternative embodiment, the supply devices for introduction ofhydrogen are designed such that the hydrogen can be introduced directlyinto the gas space of the first caverns without previously beingsaturated with sulphur. The reactor may be constructed such that it hasseveral supply devices per first cavern, some of which introducehydrogen into the sulphur melt and others introduce hydrogen directlyinto the gas space of the caverns in question. This mode of constructionallows the relative hydrogen concentration, i.e. the ratio of thehydrogen and sulphur reactants, in the first caverns to be controlled.In addition, this mode of construction can increase the amount ofhydrogen and sulphur which gets into the possible second or highercaverns described below.

In a preferred embodiment, the reactor comprises, in addition to thefirst caverns, one or more non-pressure-bearing second cavern(s) whichare arranged above the first caverns and are suitable for at leasttemporary accommodation of the product gas mixture P₁ formed in thefirst caverns and for formation of further hydrogen sulphide byexothermic reaction of sulphur and hydrogen to form a product gasmixture P₂.

A “second cavern” in the context of this invention refers to a cavernwhen at least a portion of the gas mixture which is collected in thecavern in question has flowed through at least one first cavernimmediately beforehand.

In a further embodiment, one or more of the second caverns may compriseat least one supply device suitable for controlled supply of pressurizedgaseous hydrogen. In this way, gaseous hydrogen can be introduced notjust into the first caverns but also into the second caverns inquestion, in order, for example, to increase the hydrogen concentrationin P₂ and hence the reaction rate in the second caverns in question. Thesupply devices may—as in the case of the first cavern—be constructedsuch that the hydrogen can be introduced either into the sulphur meltbelow the second caverns or directly into the gas space of the secondcaverns.

In particular embodiments, the reactor may additionally comprise one ormore non-pressure-bearing third, and optionally further, correspondinglysuitable caverns arranged above the second cavern(s).

“Third (fourth, fifth, etc.) cavern” in the context of this inventionrefers to a cavern when at least a portion of the gas mixture which iscollected in the cavern in question has flowed through at least onesecond (third, fourth, etc.) cavern immediately beforehand.

In order to enhance the hydrogen conversion in the second and highercaverns, it may be advantageous to extend the residence time of thehydrogen-containing gas mixture or to minimize the heat loss of thecaverns in question. For this purpose, the reactor may be designed suchthat at least one of the second or higher caverns has a greater volumethan each of the first caverns, and/or such that at least one of thesecond or higher caverns has lower heat removal for construction reasonsthan each of the first caverns. This is because it has been found that,in the course of operation of the reactor, more than 60% of the hydrogencan already be converted in the first cavern(s). The aforementionedmeasures can then achieve the effect that the hydrogen conversion risesto more than 80% or even more than 90% with the second cavern(s). Thehigh hydrogen conversion achieved thereby in the region of the first andsecond caverns particularly avoids the effect that the reaction proceedsin the gas space above the sulphur melt, resulting in overheating of thegas space above the sulphur melt.

The lower heat removal from a cavern for construction reasons can beachieved, for example, through use of a material with lower thermalconductivity. The cavern in question may either be manufactured fromthis material or at least parts of its surface may be lined with thismaterial. The lining may form a gas slot which additionally reduces heattransfer. Lower heat removal from individual caverns can alternativelyalso be achieved by use of a material with greater material thickness.

If a gas slot is used as an insulator, the cavern may be lined withaluminium or an aluminium alloy in order to increase the corrosionresistance of the cavern material.

In a further preferred embodiment, lower heat removal from individualcaverns is achieved by use of a cavern geometry which hinders heatremoval. For example, heat removal can be reduced by a lower ratio ofcavern surface area to cavern volume.

In a preferred embodiment, the first caverns have a ratio of surface tovolume of 1.5 to 30 m⁻¹, preferably of 3 to 9 m⁻¹, more preferably of 4to 6 m⁻¹, and/or a ratio of height to width of 0.02 to 5, preferably of0.05 to 1, more preferably of 0.08 to 0.12, and/or a ratio of weirlength to throughput of 0.1 to 10 m*h/t_(H2S), preferably of 0.2 to 1.8m*h/t_(H2S), more preferably of 1.0 to 1.2 m*h/t_(H2S). In a furtherpreferred embodiment, at least one of the second caverns has a ratio ofsurface to volume of 1.5 to 30 m⁻¹, preferably of 2.8 to 9 m⁻¹, morepreferably of 3 to 5 m⁻¹, and/or a ratio of height to width of 0.02 to5, preferably of 0.05 to 2, more preferably of 0.1 to 1, and/or a ratioof weir length to throughput of 0.1 to 10 m*h/t_(H2S), preferably of0.15 to 1.8 m*h/t_(H2S), more preferably of 0.2 to 1.1 m*h/t_(H2S).

During reactor operation, the product gas mixture P_(u) collects abovethe sulphur melt and passes from there into the gas collecting region ofthe reactor. In a preferred embodiment of the reactor, the gascollecting region is arranged above the lower reactor region. Inalternative embodiments the gas collecting region may, for example, alsobe arranged below the lower reactor region, within the lower reactorregion or at the side of the lower reactor region.

In a preferred embodiment, the reactor additionally comprises one ormore non-pressure-bearing installed device(s) suitable for continuoustransfer of the total amount of product gas mixture P_(u) formed in thelower reactor region to the gas collecting region and, in the case thata catalyst is present in the installed device(s), suitable for reactionof sulphur and hydrogen still present in the product gas mixture P_(u)to hydrogen sulphide.

The one or more installed device(s) preferably take the form of U-shapedtubes. The reactor may comprise several identical or similarlyconstructed tubes for transfer of the product gas mixture. The U-shapedtubes are typically arranged horizontally in the reactor, with each ofthe two ends pointing upward. If the gas collecting region is arrangedabove the lower reactor region, the tubes may be connected to anintermediate tray which divides the lower reactor region from the gascollecting region, such that the ends of each of the tubes project intothe gas collecting region, while the U-shaped parts of the tubes arewithin the lower reactor region. The limbs of the individual tubes mayalso be of different lengths, such that the ends of the shorter legs arewithin the lower reactor region and the ends of the longer legs projectinto the gas collecting region.

In an alternative embodiment of the reactor, the one or more installeddevice(s) take the form of straight, vertical tubes. The straight tubesare preferably arranged such that they, if the lower reactor regioncontains a sulphur melt, dip into the sulphur melt and connect the gasspace above the sulphur melt to the gas collecting region arrangedwithin or below the lower reactor region.

The tubes preferably have a diameter of 20 to 3000 mm, preferably of 60to 150 mm, more preferably of 80 to 120 mm. Through orifices which maybe provided, for example, in the side wall of a tube or, in the case ofU-shaped tubes with limbs of unequal length, at the end of the shorterlimb, the product gas mixture P_(u) passes from the lower reactor regioninto the tubes. The orifices are preferably arranged at a distance of0.1 to 3 m, preferably of 0.4 to 1.4 m, above the phase boundary of thesulphur melt, in order to prevent introduction of liquid sulphur intothe tubes. The product gas mixture flows along the tubes and passesthrough orifices mounted, for example, at the end of the tubes into thegas collecting region.

The one or more installed device(s) preferably contain a heterogeneouscatalyst for further conversion of hydrogen and sulphur present in theproduct gas P_(u) to hydrogen sulphide. Typically, a cobalt- andmolybdenum-containing catalyst is used. This is preferably asulphur-resistant hydrogenation catalyst which preferably consists of asupport, for example silica, alumina, zirconia or titania, and comprisesone or more of the active metals molybdenum, nickel, tungsten, iron,vanadium, cobalt, sulphur, selenium, phosphorus, arsenic, antimony andbismuth. Particular preference is given to a mixed compound composed ofCoO, MoO₃, and Al₂O₃ with or without sulphate in tablet form. Thecatalyst is preferably positioned in the form of a fixed bed. In thatcase, the heterogeneous catalyst takes the form of pellets, tablets orcomparable shaped bodies. However, other designs are also possible, forexample honeycombs or a fluidized bed. The catalyst may likewise bepresent in the installed devices as a coating on random packings,monoliths or knits.

The amount of catalyst positioned in the installed devices is guided bythe amount of residual hydrogen to be converted, the dimensions of theinstalled devices, the type of catalyst and possibly further factors. Inthe case of a catalyst bed, the amount of catalyst used, depending onthe amount of hydrogen supplied, should be such that the hydrogen loaddoes not exceed a value of 4000 m³ (STP) (H₂)/(m³ (catalyst bedvolume)·h).

In addition, further catalysts may be provided at one or more sites inthe reaction vessel. In this case, the catalyst is preferably positionedsuch that it does not come into contact with the liquid sulphur. Thiscatalyst may be in the form of pellet beds, of suspended powder in theliquid sulphur, or of a coating on random packings, monoliths or knits.If further catalyst is used, this catalyst may be provided in theinternals acting as caverns. In a further embodiment, this catalyst maybe provided above the liquid sulphur and all caverns.

In a preferred embodiment of the invention, at least one of theinstalled devices for transfer of the product gas mixture P_(u) from thelower reactor region to the gas collecting region is arranged in termsof construction such that, after sufficient filling of the lower reactorregion with a sulphur melt, it is in thermal contact with the sulphurmelt such that, if the installed device contains a catalyst, thecatalyst is cooled by transfer of heat to the sulphur melt. In the caseof the above-described U-shaped or straight tubes, these are preferablydesigned such that the outer shell area, in the region of the tubefilled with catalyst, is surrounded by the sulphur melt to an extent ofmore than 20%, preferably to an extent of more than 50%, more preferablyto an extent of more than 75%.

In order to ensure substantially homogeneous temperature distributionwithin the reactor, the reactor preferably comprises an inner wallwhich, in the course of operation of the reactor, with involvement ofthe space between outer reactor wall and the inner wall, allowscontinuous circulation of the sulphur melt according to the airlift pumpprinciple. Sulphur flows here, driven by the introduction of hydrogenfrom the base, upward within the reactor region surrounded by the innerwall, and flows to the base within the space between outer reactor walland the inner wall. The sulphur flowing downward can be cooled byremoval of heat via the outer reactor wall. In a preferred embodiment,the cooling of the sulphur flowing downward is supported by heatexchangers provided, for example, on the outer reactor wall or in thespace between outer reactor wall and inner wall.

In a preferred embodiment, the reactor comprises a reflux condensersuitable for condensation of the sulphur present in the product gasmixture P_(final). The reflux condenser is preferably arranged above thegas collecting region. The reflux condenser is connected to the gascollecting region via an input line suitable for transport of theproduct gas mixture P_(final) from the gas collecting region to thereflux condenser, and has a return line suitable for return of thecondensed sulphur to the reactor, preferably to the lower reactorregion. The return of the condensed sulphur also serves to cool thesulphur melt and thus contributes to maintenance of a constanttemperature of the sulphur melt.

Even in the course of long operation for several years or decades, thereactor according to the invention has to be maintained or repaired onlyinfrequently. The construction according to the invention avoids theoccurrence of excess temperatures in pressure-bearing parts and thusincreases plant safety, because reduced corrosion in this regionminimizes the risk of material failure and the probability of accidentsresulting from the escape of hazardous substances, for example hydrogensulphide. The low inspection, maintenance and repair demands lower thecosts and improve availability.

The present invention also provides a process for preparing hydrogensulphide by exothermic reaction of sulphur with hydrogen at elevatedtemperature and elevated pressure relative to standard conditions toform a product gas mixture P_(final) comprising hydrogen sulphide andsulphur, said process comprising the following steps:

-   -   providing a sulphur melt in a lower reactor region of a        pressurized reactor,    -   supplying pressurized hydrogen into the sulphur melt, the        hydrogen supplied being accommodated at least partly, together        with sulphur converted from the sulphur melt to the gaseous        state, by at least two non-pressure-bearing first caverns,    -   at least temporarily leaving the hydrogen and the sulphur in the        first caverns, so as to form, in exothermic reaction, a product        gas mixture P₁ comprising hydrogen sulphide, sulphur and        hydrogen,    -   at least temporarily leaving the product gas mixture P₁ formed        in the first caverns in one or more second cavern(s), so as to        react the sulphur and hydrogen present in the product gas        mixture P₁ with formation of further hydrogen sulphide to give a        product gas mixture P₂, and    -   collecting the product gas mixture P_(final) in a gas collecting        region.

The process is preferably performed in the reactor according to theinvention already described.

Rather than pure hydrogen, it is also possible to pass contaminatedhydrogen through the sulphur melt. The impurities may, for example, becarbon dioxide, hydrogen sulphide, water, methanol, methane, ethane,propane or other volatile hydrocarbons. Preference is given to usinghydrogen having a purity greater than 65% based on the gas volume. Theimpurities in the hydrogen or reaction products thereof are preferablynot removed before the synthesis of methyl mercaptan, but left in thereactant mixture. The sulphur used may also contain differentimpurities.

The pressure and volume of the hydrogen supplied are guided by thepressure at which the reactor is operated and the volume of hydrogenrequired. The amount of sulphur used is virtually stoichiometric to theamount of hydrogen used. Spent sulphur is replenished during theprocess.

In a preferred embodiment of the process, the product gas mixture isaccommodated in at least one second cavern and is left at leasttemporarily therein, so as to react the sulphur and hydrogen present inthe product gas mixture P₁ with formation of further hydrogen sulphideto give the product gas mixture P₂.

In a further embodiment of the process, at least a portion of thehydrogen supplied into the sulphur melt is accommodated directly by atleast one of the second caverns. “Directly” is understood here to meanthat the hydrogen supplied is not accommodated by a first cavern beforepassing into a second cavern. The hydrogen supply can thus be controlledwith the aim of influencing the reaction rate in the first and secondcaverns in different ways.

The process can be performed in such a way that the product gas mixtureis accommodated and left at least temporarily in at least one third orhigher cavern, so as to react the sulphur and hydrogen present in theproduct gas mixture P₂ with formation of further hydrogen sulphide.

In an alternative embodiment of the process, at least some of thehydrogen is supplied at least to the first and/or higher caverns suchthat it does not come into contact with the sulphur melt beforehand.This can increase the hydrogen concentration in the caverns in questionwithout also simultaneously transferring additional sulphur to the gasspace of the cavern.

The supply of hydrogen into the liquid sulphur below a cavern (forexample a second cavern) firstly has the effect that the hydrogensupplied to this cavern is increased, and secondly that sulphur is alsotransferred from the liquid sulphur to the gas space of this cavern.

In one embodiment of the process, the total amount of the product gasmixture P_(u) formed in the lower reactor region is continuouslytransferred to the gas collecting region by means of one or morenon-pressure-bearing installed device(s), wherein by use of a catalystin the installed device(s) the sulphur and hydrogen present in theproduct gas mixture P_(u) are reacted with formation of further hydrogensulphide.

The process is preferably performed such that the heat of reactionreleased by the reaction of sulphur and hydrogen is released into thesulphur melt as completely as possible. This includes the heat ofreaction released over the catalyst. Preferably, heat transfer of theheat of reaction, released by the reaction of sulphur and hydrogen inthe catalyst, to the sulphur melt thus cools the catalyst.

The process is preferably performed in such a way that the proportion ofhydrogen sulphide in the product gas mixture prior P_(u) to introductioninto the installed device(s) containing the catalyst is at least 60%,preferably at least 90%, of the gas volume. The process conditionsrequired for this purpose are described below. This has the advantagethat the low proportion of hydrogen in the region of the catalystprevents overheating of the catalyst and thus increases the service lifeof the catalyst.

The process preferably comprises an additional process step in which thesulphur present in the product gas mixture P_(final) is condensed andrecycled directly into the reactor, preferably to the lower reactorregion. As a result there is the advantageous effect that cooling of thesulphur melt takes place as a function of the amount of hydrogensulphide produced. More particularly, at the moment at which thetemperature of the sulphur melt rises, there is likewise an increase inthe hydrogen conversion, sulphur vaporization and sulphur reflux, suchthat overheating of the sulphur melt is counteracted. The sulphurcondensation is preferably effected at a temperature of 120 to 150° C.

The process according to the invention can typically be performed at apressure of 1 to 30 bar, preferably at 5 to 15 bar, more preferably 7 to12 bar. The temperature of the sulphur melt is typically 300 to 600° C.,preferably 380 to 480° C., more preferably 400 to 450° C. Hydrogenconversions of 99.9% are thus easily achievable. Hydrogen conversions inthe region of 99.93% have likewise been observed.

The process according to the invention enables the production ofhydrogen sulphide having a purity of more than 99.8% by volume. A purityof up to 99.85% by volume has likewise been found. In this case, theproduct gas mixture, after condensation of sulphur present, may containbetween 0.05 and 0.15% by volume of hydrogen, 10 to 30 ppm of sulphurand 400 to 600 ppm of sulphanes. Sulphanes in the context of thisinvention refer to hydrogen polysulphides according to the empiricalformula H₂S_(x) where x is typically an integer from 2 to 10. Theabovementioned sulphur concentrations are already enabled by sulphurcondensation within the abovementioned temperature range. Freezing attemperatures below 120° C.—as known from other H₂S processes—is notrequired for this purpose.

The present invention also relates to the use of a reactor according tothe invention for preparation of hydrogen sulphide having a sulphanecontent not exceeding 600 ppm, preferably not exceeding 400 ppm, morepreferably not exceeding 200 ppm.

The present invention is further described by the following examples:

-   -   1. Reactor (1) suitable for continuous preparation of hydrogen        sulphide by exothermic reaction of sulphur and hydrogen to form        a final product gas mixture P_(final) comprising hydrogen        sulphide and sulphur at elevated temperature and elevated        pressure relative to standard conditions, said reactor (1)        comprising        -   a lower reactor region (2) suitable for accommodating a            sulphur melt (3), and        -   a gas collecting region (6) suitable for accommodating the            product gas mixture P_(final) at elevated temperature and            elevated pressure relative to standard conditions,        -   characterized in that the reactor (1) comprises at least two            non-pressure-bearing first caverns (4) and at least one            supply device (5, 5 a) suitable for controlled supply of            pressurized gaseous hydrogen per first cavern, said caverns            (4) being suitable for at least temporary accommodation of a            product gas mixture P₁ which forms in exothermic reaction            and comprises hydrogen sulphide, sulphur and hydrogen.    -   2. Reactor according to Example 1, characterized in that the        reactor (1) additionally comprises one or more non-pressure        bearing second cavern(s) (8) which are arranged above the first        cavern(s) (4) and are suitable for at least temporary        accommodation of the product gas mixture P₁ formed in the first        cavern(s) (4) and for formation of further hydrogen sulphide by        exothermic reaction of sulphur and hydrogen to form a product        gas mixture P₂.    -   3. Reactor according to Example 2, characterized in that at        least one of the second caverns (8) comprises at least one        supply device (9, 9 a) suitable for controlled supply of        pressurized gaseous hydrogen.    -   4. Reactor according to Example 2 or 3, characterized in that        the reactor (1) additionally comprises one or more        non-pressure-bearing third (10), and optionally further,        correspondingly suitable caverns arranged above the second        cavern(s) (8).    -   5. Reactor according to any one of Examples 2 to 4,        characterized in that at least one of the second or higher        caverns (8, 10) has a greater volume than each of the first        caverns (4), and/or in that at least one of the second or higher        caverns (8, 10) has lower heat removal for construction reasons        than each of the first caverns (4).    -   6. Reactor according to any one of Examples 1 to 5,        characterized in that the reactor (1) additionally comprises one        or more non-pressure-bearing installed device(s) (7) suitable        for continuous transfer of the total amount of product gas        mixture P_(u) formed in the lower reactor region (2) to the gas        collecting region (6) and, in the case that a catalyst is        present in the installed device(s) (7), suitable for reaction of        sulphur and hydrogen still present in the product gas mixture        P_(u) to hydrogen sulphide.    -   7. Reactor according to Example 6, characterized in that one,        more than one or all of the installed devices (7) for transfer        of the product gas mixture P_(u) from the lower reactor region        (2) to the gas collecting region (6) are arranged in terms of        construction such that, after sufficient filling of the lower        reactor region (2) with a sulphur melt (3), they are in thermal        contact with the sulphur melt (3) such that, if the installed        device (7) contains a catalyst, the catalyst is cooled by        transfer of heat to the sulphur melt (3).    -   8. Reactor according to any one of Examples 1 to 7,        characterized in that the reactor comprises an inner wall (11)        which, in the course of operation of the reactor with        involvement of the space between outer reactor wall and the        inner wall (11), allows continuous circulation of the sulphur        melt according to the airlift pump principle.    -   9. Reactor according to any one of Examples 1 to 8,        characterized in that the reactor additionally comprises        -   a reflux condenser suitable for condensation of the sulphur            present in the product gas mixture P_(final),        -   an input line suitable for transport of the product gas            mixture P_(final) from the gas collecting region to the            reflux condenser and        -   a return line suitable for return of the condensed sulphur            to the reactor.    -   10. Process for preparing hydrogen sulphide by exothermic        reaction of sulphur with hydrogen at elevated temperature and        elevated pressure relative to standard conditions to form a        product gas mixture P_(final) comprising hydrogen sulphide and        sulphur, said process comprising the following steps:        -   providing a sulphur melt in a lower reactor region of a            pressurized reactor,        -   supplying pressurized hydrogen into the sulphur melt, the            hydrogen supplied being accommodated at least partly,            together with sulphur converted from the sulphur melt to the            gaseous state, by at least two non-pressure-bearing first            caverns,        -   at least temporarily leaving the hydrogen and the sulphur in            the first caverns, so as to form, in exothermic reaction, a            product gas mixture P₁ comprising hydrogen sulphide, sulphur            and hydrogen, and        -   collecting the product gas mixture P_(final) in a gas            collecting region.    -   11. Process according to Example 10, characterized in that the        product gas mixture P₁ is left at least temporarily in one or        more second cavern(s), so as to react the sulphur and hydrogen        present in the product gas mixture P₁ with formation of further        hydrogen sulphide to give a product gas mixture P₂.    -   12. Process according to Example 11, characterized in that at        least a portion of the hydrogen supplied into the sulphur melt        is accommodated directly by one or more second cavern(s).    -   13. Process according to Example 11 or 12, characterized in that        the product gas mixture is accommodated and left at least        temporarily in one or more third or higher cavern(s), so as to        react the sulphur and hydrogen present in the product gas        mixture P₂ with formation of further hydrogen sulphide.    -   14. Process according to any one of Examples 10 to 13,        characterized in that the total amount of the product gas        mixture P_(u) formed in the lower reactor region is continuously        transferred to the gas collecting region by means of one or more        non-pressure-bearing installed device(s), wherein by use of a        catalyst in the installed device(s) the sulphur and hydrogen        present in the product gas mixture P_(u) are reacted with        formation of further hydrogen sulphide.    -   15. Process according to Example 14, characterized in that the        catalyst is cooled by heat transfer of the heat of reaction,        released by the reaction of sulphur and hydrogen in the        catalyst, to the sulphur melt.    -   16. Process according to Example 14 or 15, characterized in that        the proportion of hydrogen sulphide in the product gas mixture        P_(u) prior to introduction into the installed device(s)        containing the catalyst is at least 60% of the gas volume.    -   17. Process according to any one of Examples 10 to 16,        characterized in that it comprises an additional process step in        which the sulphur present in the product gas mixture P_(final)        is condensed and recycled directly into the reactor.    -   18. Process according to any one of Examples 10 to 17,        characterized in that the preparation of hydrogen sulphide is        performed at a pressure of 5 to 15 bar.    -   19. Process according to any one of Examples 10 to 18,        characterized in that the temperature of the sulphur melt is 400        to 450° C.    -   20. Process according to any one of Examples 10 to 19,        characterized in that the sulphur melt is circulated        continuously according to the airlift pump principle.    -   21. Use of a reactor according to any one of Examples 1 to 9 for        preparation of hydrogen sulphide having a sulphane content not        exceeding 600 ppm.

FIG. 1 shows, by way of example and schematically, a reactor which canbe used in accordance with the invention for preparation of hydrogensulphide from hydrogen and sulphur.

The reactor 1, shown in FIG. 1, comprises an outer, pressure-bearingvessel containing a sulphur melt 3 in the lower region 2 thereof. Bymeans of supply devices 5, hydrogen can be introduced into the sulphurmelt, and is accommodated directly by the first caverns 4. Supplydevices 5 a can also be used to introduce hydrogen directly into the gasspace 12 of the first caverns 4. In the gas space 12 of the firstcaverns 4, the product gas mixture P₁ comprising hydrogen, sulphur andhydrogen sulphide is formed. The reactor shown also has additionalsupply devices 9, by means of which hydrogen can be supplied directly tothe second caverns 8, wherein the product gas mixture P₂ forms in thegas space 13. By means of supply devices 9 a, hydrogen can also beintroduced directly into the gas space 13 of the second caverns 8. Thegas mixture flowing upward is temporarily accommodated by the thirdcaverns 10, wherein the product gas mixture P₃ forms in the gas space14. In the gas space 15, the entire product gas mixture P_(u) formed inthe lower reactor region collects. The gas space 15 is separated fromthe gas collecting region 6 by an intermediate tray 16. The product gasmixture P_(u) is transferred from the gas space 15 to the gas collectingregion 6 using the installed device 7. The installed device 7 isdesigned as a U-shaped tube which dips into the sulphur melt 3. Viaorifices 17 and 18, gas can flow into and out of the installed device 7.The installed device 7 can accommodate a catalyst which enables thefurther conversion of sulphur and hydrogen in the product gas mixtureP_(u) to form the product gas mixture P_(final). The product gas mixtureP_(final) comprising sulphur and hydrogen sulphide is accommodated inthe gas collecting region 6 and can be withdrawn from the reactor viathe orifice 19, or optionally supplied to a reflux condenser. In theregion of the sulphur melt, the reactor also comprises an inner wall 11which serves for continuous circulation of the sulphur melt according tothe airlift pump principle.

FIG. 2 shows a schematic of four different illustrative cavernarrangements in the case of a reactor with first, second and thirdcaverns. The caverns consist of intermediate trays each having oneorifice. The orifices are each arranged such that the gas mixture mustflow from the first to the second and from the second to the thirdcavern. Top left is a reactor according to the invention with a first,second and third cavern in each case. The three caverns each have thesame geometry. Top right is a reactor according to the invention with afirst, second and third cavern in each case, with continuouslyincreasing weir height and hence increasing residence time of the gasmixture from the first to the third cavern. Bottom left is a reactoraccording to the invention with a first, second and third cavern in eachcase, all caverns having the same weir height. The second cavern has acircular orifice in the middle of the intermediate tray. Bottom right isa reactor according to the invention with a first, second and thirdcavern in each case, with continuously increasing weir height and henceincreasing residence time of the gas mixture from the first to the thirdcavern.

FIG. 3 shows a schematic of illustrative embodiments of caverns. Thecaverns shown have an intermediate tray with a weir running along theedge thereof. Various embodiments are shown for the lower edge of theweir A and the profile of the weir B.

EXAMPLES Example 1 Comparative Example

1000 l (STP)/h of hydrogen were introduced continuously via a frit atthe base into a tube having an internal diameter of 5 cm which had beenfilled with liquid sulphur up to a height of 1 m. The consumption ofsulphur was compensated for by further metered addition of liquidsulphur, while keeping the fill level constant. Sulphur removed from theproduct gas stream by condensation was recycled into the upper region ofthe tube in liquid form. Above the liquid sulphur, jacketedthermocouples for temperature measurement were provided at intervals of10 cm. While the reactor was heated to 400° C. electrically via theouter wall, a homogeneous temperature of about 397° C. was presentwithin the sulphur. However, the thermocouples above the sulphur showeda maximum temperature of 520° C. In addition, above the liquid sulphur,new material samples made from standard stainless steel (1.4571) wereprovided at the location of maximum temperature. After an operating timeof about 400 h, the material samples were removed and showed severecorrosion phenomena in the form of flaking and weight loss.

Example 2 Comparative Example

Example 1 was repeated, except that the height of the liquid sulphur wasraised to 4 m. The value of the maximum temperature above the liquidsulphur was maintained. Severe corrosion phenomena likewise occurred onthe material samples.

Example 3 Comparative Example

Example 2 was repeated, except that 15% by weight of a pulverulentCo₃O₄MoO₃/Al₂O₃ catalyst were suspended in liquid sulphur. The value ofthe maximum temperature above the liquid sulphur was maintained. Severecorrosion phenomena likewise occurred on the material samples.

Example 4 Comparative Example

The preparation of hydrogen sulphide was performed in a pilot plant. Thepilot reactor had a height of approx. 5.5 m, a diameter of approx. 0.5 mand a volume of approx. 0.8 m³. The pilot plant was equipped with fourcaverns of equal dimensions in series. 70 m³ (STP)/h of hydrogen weremetered in continuously via the hydrogen feeds, which corresponded to ahydrogen load of 3700 m³ (STP)(H₂)/(m³ (cavern volume)·h) based on thesingle cavern. Spent sulphur was replenished under fill level control.Sulphur removed from the product gas stream by condensation was recycledinto the reactor in liquid form. The pressure in the reactor was 12 bar.The temperature in the liquid sulphur was 430° C. The residence time inthe caverns was 5 s in each case. The H₂ conversion through homogeneousreaction in the caverns was about 90%. By means of thermocouplesinstalled in a fixed manner in the reactor, the temperature within thecaverns and above the sulphur melt was measured. The highest temperaturemeasured in the caverns under these circumstances was 479° C. Above theliquid sulphur phase, no commencement of a homogeneous reaction wasdiscernible. The gas temperature above the liquid sulphur correspondedvirtually to the temperature of the liquid sulphur, such that there wereno increased demands on the material of the pressure-bearing jacket inthe region of the gas phase above the liquid sulphur.

The gas phase then flowed to and through the catalyst in the installeddevice, as shown schematically in FIG. 1 (7). The hydrogen remaining wasthen converted virtually completely over the catalyst (overallconversion of H₂: 99.86 mol %). The gas hourly space velocity on thecatalyst was 3700 m³ (STP)(H₂)/(m³ (bed volume of catalyst)·h). Therewas virtually no occurrence of corrosion in the form of flaking orweight loss on the material used. Material samples made from standardstainless steel (1.4571) which were installed for comparative purposeshad only moderate corrosion attack.

LIST OF REFERENCE NUMERALS

-   (1) Reactor-   (2) Lower reactor region-   (3) Sulphur melt-   (4) First caverns-   (5, 5 a) Hydrogen supply device to the first caverns-   (6) Gas collecting region-   (7) Installed device for transfer of gas from the lower reactor    region to the gas collecting region, optionally containing a    catalyst-   (8) Second caverns-   (9, 9 a) Hydrogen supply device to the second caverns-   (10) Third caverns-   (11) Inner wall-   (12) Gas space of the first caverns-   (13) Gas space of the second caverns-   (14) Gas space of the third caverns-   (15) Gas space of the lower reactor region-   (16) Intermediate tray-   (17) Orifice-   (18) Orifice-   (19) Orifice

The invention claimed is:
 1. A reactor for continuous preparation ofhydrogen sulphide by exothermic reaction of sulphur and hydrogen to forma final product gas mixture P_(final) comprising hydrogen sulphide andsulphur at elevated temperature and elevated pressure relative tostandard conditions, said reactor, comprising: a lower reactor regionincluding a sulphur melt, and a gas collecting region configured foraccommodating a product gas mixture P_(final) at elevated temperatureand elevated pressure relative to standard conditions, wherein thereactor comprises at least two non-pressure-bearing first caverns and asupply device providing a controlled supply of pressurized gaseoushydrogen to the lower reactor region per first caverns, the cavernsbeing configured for at least temporary accommodation of a product gasmixture P₁ which forms in exothermic reaction and comprises hydrogensulphide, sulphur and hydrogen, and the reactor additionally comprises anon-pressure-bearing second cavern which is arranged above the firstcavern and is configured for at least temporary accommodation of theproduct gas mixture P₁ formed in the first cavern and for formation offurther hydrogen sulphide by exothermic reaction of sulphur and hydrogento form a product gas mixture P₂.
 2. The reactor according to claim 1,wherein at least one of the second caverns comprises at least one supplydevice suitable for controlled supply of pressurized gaseous hydrogen.3. The reactor according to claim 1, wherein the reactor additionallycomprises a non-pressure-bearing third cavern, and optionally further,correspondingly suitable caverns arranged above the second cavern. 4.The reactor according to claim 3, wherein at least one of thepressure-bearing third or further suitable caverns has a greater volumethan each of the first caverns, and/or in that at least one of thepressure-bearing third or further suitable caverns has lower heatremoval for construction reasons than each of the first caverns.
 5. Thereactor according to claim 1, wherein the reactor additionally comprisesa non-pressure-bearing installed device configured for continuoustransfer of the total amount of product gas mixture P_(u) formed in thelower reactor region to the gas collecting region and, in the case thata catalyst is present in the installed device, the device is configuredfor reaction of sulphur and hydrogen still present in the product gasmixture P_(u) to hydrogen sulphide.
 6. The reactor according to claim 5,wherein one, more than one or all of the installed devices for transferof the product gas mixture Pu from the lower reactor region to the gascollecting region are arranged in terms of construction such that, aftersufficient filling of the lower reactor region with a sulphur melt, theyare in thermal contact with the sulphur melt such that, when theinstalled device contains a catalyst, the catalyst is cooled by transferof heat to the sulphur melt.
 7. The reactor according to claim 1,wherein the reactor comprises an inner wall which, in the course ofoperation of the reactor with involvement of the space between outerreactor wall and the inner wall, obtains continuous circulation of thesulphur melt according to the airlift pump principle.
 8. The reactoraccording to claim 1, wherein the reactor additionally comprises: areflux condenser configured for condensation of the sulphur present inthe product gas mixture P_(final), an input line configured fortransport of the product gas mixture P_(final) from the gas collectingregion to the reflux condenser and a return line configured for returnof the condensed sulphur to the reactor.
 9. A process for preparinghydrogen sulphide by exothermic reaction of sulphur with hydrogen atelevated temperature and elevated pressure relative to standardconditions to form a product gas mixture P_(final) comprising hydrogensulphide and sulphur, the process comprising: supplying pressurizedhydrogen into a sulphur melt located in a lower reactor region of apressurized reactor, the hydrogen supplied being accommodated at leastpartly, together with sulphur converted from the sulphur melt to thegaseous state, by at least two non-pressure-bearing first caverns,wherein the pressurized gaseous hydrogen is supplied by supply devicesper first caverns; at least temporarily leaving the hydrogen and thesulphur in the first caverns, so as to form, in exothermic reaction, aproduct gas mixture P₁ comprising hydrogen sulphide, sulphur andhydrogen; at least temporarily leaving the product gas mixture P₁ formedin the first caverns in a second cavern, so as to react the sulphur andhydrogen present in the product gas mixture P₁ with formation of furtherhydrogen sulphide to give a product gas mixture P₂ and collecting theproduct gas mixture P_(final) in a gas collecting region.
 10. Theprocess according to claim 9, wherein at least a portion of the hydrogensupplied into the sulphur melt is accommodated directly by the secondcavern.
 11. The process according to claim 9, wherein the product gasmixture is accommodated and left at least temporarily in a third orhigher cavern, so as to react the sulphur and hydrogen present in theproduct gas mixture P₂ with formation of further hydrogen sulphide. 12.The process according to claim 9, wherein the total amount of theproduct gas mixture P_(u) formed in the lower reactor region iscontinuously transferred to the gas collecting region by anon-pressure-bearing installed device, wherein by use of a catalyst inthe installed device the sulphur and hydrogen present in the product gasmixture P_(u) are reacted with formation of further hydrogen sulphide.13. The process according to claim 12, wherein the catalyst is cooled byheat transfer of the heat of reaction, released by the reaction ofsulphur and hydrogen in the catalyst, to the sulphur melt.
 14. Theprocess according to claim 12, wherein the proportion of hydrogensulphide in the product gas mixture P_(u) prior to introduction into theinstalled device containing the catalyst is at least 60% of the gasvolume.
 15. The process according to claim 9, further comprisingcondensing and recycling directly into the reaction, sulphur present inthe product gas mixture P_(final).
 16. The process according to claim 9,wherein the preparation of hydrogen sulphide is performed at a pressureof 5 to 15 bar.
 17. The process according to claim 9, wherein thetemperature of the sulphur melt is 400 to 450° C.
 18. The processaccording to claim 9, wherein the sulphur melt is circulatedcontinuously according to the airlift pump principle.
 19. The processaccording to claim 9, wherein the hydrogen sulphide has a sulphanecontent not exceeding 600 ppm.